The invention relates to fluid-operated regulating apparatus, especially for use in motor vehicles, and more particularly to improvements in hydraulic or pneumatic apparatus wherein at least one valve, such as a magnetic valve, is adjustable by control means to vary the characteristics of a fluid in a path leading from a pump or another suitable fluid displacing and pressurizing machine to at least one consumer. The valve can be set up to act as a proportional valve, an on-off valve or a multi-way cock.
It is known to resort to pulse-width modulation as a method of controlling the manner in which a valve can influence a pressurized fluid in a path between a source of pressurized fluid and one or more consumers. Such mode of regulation was proposed for the purpose of achieving a reduction of hysteresis. It is also known to achieve a reduction of hysteresis by applying to a valve control signals which are subject to oscillation. Still further, it is known to employ a valve which is influenced by signals subject to frequency changes within the regulating range.
As a rule, hysteresis which develops when a valve is employed in a fluid-operated regulating apparatus exerts an adverse influence upon the operation of such apparatus. On the other hand, if the operation of the valve is controlled by resorting to a control value or parameter having a given frequency which has been found to be desirable because it exerts a positive influence upon the hysteresis, one is likely to adversely influence the mechanical characteristics of the valve. For example, if the valve is controlled by resorting to a low-frequency signal, the valving element is likely to impact upon the seat with a highly pronounced force (chatter). On the other hand, if the chosen frequency of a valve-controlling or regulating signal is too high, the inertia of the mass of the mobile valving element, such as a reciprocable piston or plunger, is likely to be too large to permit the valving element to follow the high-frequency changes of such signals.